The disclosure of the present patent application pertains to a ceramic body that contains alumina and boron carbide, as well as a method of making the same and a method of using the same. More specifically, the disclosure of the present patent application pertains to a ceramic body (for use as a ceramic cutting insert or a substrate for a coated ceramic cutting insert or a ceramic wear part) that contains alumina and a boron carbide phase, as well as a method (e.g., hot pressing method or a pressureless sintering-HIPping method) of making the same and a method of using the same.
Ceramic materials have been used as cutting inserts and as wear members for a number of years. These ceramic materials include silicon nitride or silicon nitride-based ceramics, SiAlON or SiAlON-based ceramics, and alumina or alumina-based ceramics. One of the first ceramic cutting inserts was an alumina cutting insert. See Dörre et al., “Alumina, Processing, Properties, and Applications”, Springer-Verlag (1984), pages 254-265. The alumina cutting insert was essentially over 99.7 percent alumina. Later on, the alumina ceramic was modified by the addition of titanium carbide. See Whitney, “Modern Ceramic Cutting Tool Materials”, Presentation at October, 1982 ASM Metals Congress in St. Louis, Mo.
Over the passage of time, there have been a number of other additives used in conjunction with alumina to form an alumina-based ceramic cutting insert. Examples of the additives include the use of silicon carbide whiskers such as the ceramics that appear to be disclosed in the U.S. Pat. No. 4,789,277 to Rhodes et al. and U.S. Pat. No. 4,961,757 to Rhodes et al. In an alumina-SiC whisker ceramic, the Rhodes et al. patents appears to show that the (KIC) fracture toughness increased (4.15 to 8.9 MPa·m0.5) as the SiC whisker content increased from 0 to 24 volume percent. The Rhodes et al. patents then appear to show that the fracture toughness decreased (8.9 to 7.6 MPa·m0.5) as the SiC whisker content increased from 24 to 35 volume percent. European Patent No. 0 335 602 B1 to Lauder appears to disclose the use of silicon carbide whiskers in alumina along with the addition of additives like zirconia, yttria, hafnia, magnesia, lanthana or other rare earth oxides, silicon nitride, titanium carbide, titanium nitride or mixtures thereof. The use of silicon carbide whiskers along with alumina is described in Billman et al., “Machining with Al2O3—SiC Whisker Cutting Tools”, Ceramic Bulletin, Vol. 67, No. 6 (1988) pages 1016-1019. U.S. Pat. No. 4,343,909 to Adams et al. appears to disclose the use of zirconia and titanium diboride along with alumina (and a sintering aid). U.S. Pat. No. 4,543,343 to Iyori et al. discloses the use of titanium boride and zirconia along with alumina.
In the article written by Liu and Ownby (Liu et al. entitled “Physical Properties of Alumina-Boron Carbide Whisker/Particle Composites” Ceramic Eng. Sci. Proc. 12 (7-8) pp. 1245-1253 (1991) there is a disclosure of a ceramic comprising alumina and boron carbide particles. In this regard, the Liu et al. composites appear to disclose alumina (A16SG from Alcoa)-boron carbide particle (0.2 to 7 μm particles size) composites along with boron carbide that is present in amounts of 5.0, 10.0, 15.0 and 20.0 volume percent (the balance equals alumina). The examples were either sintered at 1500° C. or 1600° C. for 3 hours or hot-pressed under the hot pressing parameters that comprised a temperature equal to 1520° C. for a duration equal to 20 minutes. The sintered composites had a density less than 80 percent of the theoretical density. The hot pressed ceramics had a density of greater than 98 percent of the theoretical density. The hot pressing pressure seems to be absent from the disclosures of this Liu et al. article.
This Liu et al. article appears to show that the fracture toughness (measured by the Chevron Notched Short Rod (CNSR) technique) improves from 0 volume percent boron carbide particles to 5.0 volume percent boron carbide particles wherein the fracture toughness of the 5.0 volume percent boron carbide particle-alumina ceramic equals about 5.2 MPa·m0.5. However, the fracture toughness drops off at boron carbide particle contents greater than 5.0 volume percent. More specifically, the fracture toughness diminishes at boron carbide particle contents of 10.0, 15.0 and 20.0 volume percent. The fracture toughness of the 20.0 volume percent boron carbide particle-alumina ceramic appears to equal about 4.5 MPa·m0.5. Liu et al also shows that the flexural strength improves from 0 volume percent boron carbide particles to 5.0 volume percent boron carbide particles. The 5.0 volume percent boron carbide particle-alumina material has a flexural strength equal to about 575 MPa. The flexural strength levels off (i.e., remains essentially the same) at boron carbide particle contents greater than 5.0 volume percent (i.e., boron carbide particle contents of 10.0, 15.0 and 20.0 volume percent). The 20.0 volume percent boron carbide particle-alumina material has a flexural strength equal to about 590 MPa.
In the article (1991-American Institute of Physics) written by Liu et al. entitled “Boron Containing Ceramic Particulate and Whisker Enhancement of the Fracture Toughness of Ceramic Matrix Composites” there is a disclosure of a ceramic comprising alumina and boron carbide particles. These Liu et al composites appear to disclose α-alumina-boron carbide particle composites wherein the boron carbide is present in amounts of 5.0, 10.0, 15.0 and 20.0 volume percent (the balance equals alumina). The examples were hot-pressed under the hot pressing parameters that comprised a temperature equal to 1480° C. so that the ceramic had a density of greater than 98 percent of the theoretical density. The hot pressing duration and the hot pressing pressure appear to be absent from the disclosure of this Liu et al. article.
The Liu et al. articles show that the fracture toughness (CNSR technique) improves from 0 volume percent boron carbide particles to 5.0 volume percent boron carbide particles wherein the fracture toughness of the 5.0 volume percent boron carbide particle-alumina ceramic equals about 5.5 MPa·m0.5. However, the fracture toughness drops off at boron carbide particle contents greater than 5.0 volume percent. More specifically, the fracture toughness diminishes at boron carbide particle contents of 10.0, 15.0 and 20.0 volume percent. The fracture toughness of the 20.0 volume percent boron carbide particle-alumina ceramic appears to equal about 4.6 MPa·m0.5.
In the article written by Liu et al. entitled “Boron Carbide Reinforced Alumina Composites” Journal American Ceramic Society 74 (3) pp. 674-677 (1991)) there is a disclosure of a ceramic comprising alumina and boron carbide particles. The Liu et al. composites appear to disclose fine α-alumina (A16SG from Alcoa)-boron carbide “shard like” particle (0.2 to 7 μm particles size) composites along with boron carbide that is present in amounts of 5.0, 10.0, 15.0 and 20.0 volume percent (the balance equals alumina). The examples were hot-pressed under the hot pressing parameters that comprised a temperature equal to 1520° C. for duration equal to 20 minutes so that the ceramic had a density of greater than 98 percent of the theoretical density. The hot pressing pressure seems to be absent from the disclosures of the Liu et al. articles.
This Liu et al. article appears to show that the fracture toughness (CNSR technique) improves from 0 volume percent boron carbide particles to 5.0 volume percent boron carbide particles wherein the fracture toughness of the 5.0 volume percent boron carbide particle-alumina ceramic equals about 5.3 MPa·m0.5. However, the fracture toughness drops off at boron carbide particle contents greater than 5.0 volume percent. More specifically, the fracture toughness diminishes at boron carbide particle contents of 10.0, 15.0 and 20.0 volume percent. The fracture toughness of the 20.0 volume percent boron carbide particle-alumina ceramic appears to equal about 4.6 MPa·m0.5. Liu et al also shows that the flexural strength improves from 0 volume percent boron carbide particles to 5.0 volume percent boron carbide particles. The 5.0 volume percent boron carbide particle-alumina material has a flexural strength equal to about 580 MPa. The flexural strength levels off (i.e., remains essentially the same) at boron carbide particle contents greater than 5.0 volume percent (i.e., boron carbide particle contents of 10.0, 15.0 and 20.0 volume percent). The 20.0 volume percent boron carbide particle-alumina material has a flexural strength equal to about 600 MPa.
The Jung and Kim article entitled “Sintering and Characterization of Al2O3—B4C composites”, Journal of Material Science 26 (1991) pp. 5037-5040 concerns the sintering of alumina-boron carbide composites. According to the article, for composites sintered at 1850° for 60 minutes the density was about 97 percent for a boron carbide content that ranged between 5 to 20 volume percent boron carbide. According to the Jung et al. article, the flexural strength had a maximum value of 550 MPa for an alumina-20 volume percent boron carbide composite that had been sintered at 1850° for 60 minutes. According to the Jung et al. article, for a composite sintered at 1850° for 60 minutes. The Vickers micro-hardness increased with increasing boron carbide content to 30 volume percent. For this same composite, the fracture toughness slightly increases with increasing boron carbide contents up to 20 volume percent. The maximum fracture toughness is 4 MPa·m1/2.
In the article entitled “Microstructural Coarsening During Sintering of Boron Carbide” by Dole et al. (J. Am. Ceram. Soc. 72 (6) pages 958-966 (1989), it was reported that pressureless sintering of boron carbide at 2300° C. produced only limited densification due to microstructural coarsening. According to the article entitled “Pressureless Sintering of Boron Carbide” by Lee et al., J. Am. Ceram. Soc. 86(9) pages 1468-1473 (2003), improved densities for pressureless sintered boron carbide bodies were obtained via rapid heating to liquid phase sintering temperatures so as to shorten the time for coarsening to occur. Further, the addition of carbon apparently caused a reaction with the boron oxide (B2O3) coating so as to improve densification. According to the article entitled “Sintering of Boron Carbide Heat-Treated with Hydrogen” by Lee et al., J. Am. Ceram. Soc. 85(8) pages 2131-2133 (2002), hydrogen gas in the sintering atmosphere was used to extract the boron oxide coating on the boron carbide particles, and as a result, the process achieved a pressureless sintered boron carbide body that exhibited a theoretical density equal to 94.7 percent.
In the article by Dongsheng et al. entitled “Control of Boron Content During Sintering of B4C-dispersed Al2O3 Pellets” in Journal of Central South Institute of Mining and Metallurgy (October 1994) carbon is added to alumina (Al2O3) and boron carbide (B4C) to reduce the loss of boron during sintering, and thereby achieve precise control of the boron content in B4C—Al2O3 pellets. According to this article, these B4C—Al2O3 are used in nuclear reactor cores and the boron content in these pellets affects the magnitude of neutron flux in the core. The article states that the reason the carbon controls the boron content is that microparticles of carbon contained in the pellets oxidize before the B4C, and can even reduce and carbonize the B2O3 to B4C.
The article by Donsheng et al. entitled “Sintering behavior of B4C-dispersed Al2O3 Pellets” in Journal of Central South Institute of Mining and Metallurgy (February 1989) also concerned Al2O3—B4C pellets used in nuclear reactors. This article looked at the impact of particle sizes, as well as other factors, on properties of the sintered pellets.
Air Force Report AFML-TR-69-50 by E. Dow Whitney entitled “New and Improved Cutting Tool Materials” (1969) discloses an alumina-boron carbide composite. At page 119, the Report reads:                The metal carbides, WC, TaC, TiC, B4C and SiC were selected as additives for improving the general properties of hot presses alumina. Mixtures of Al2O3 containing 1.25 wt. % of each additive were hot pressed at 1600° C., 2600 psi, for 30 minutes in a nitrogen atmosphere. In FIGS. 147 to 149 are shown the heating densification curves of these systems. Density increased rapidly from about 1200° C. and reached almost 100% relative density at temperatures below 1600° C.Table 52 of the Air Force Report appears to show that the addition of 1.25 weight percent boron carbide to alumina increased the MOR from 30,700 psi (for alumina) to 42,500 psi (alumina+1.25 weight percent boron carbide), but the hardness decreased from 94.2 (RN15) to 93.7 (RN15).        
U.S. Pat. No. 5,271,758 to Buljan et al. pertains to an alumina-based composite that can include boron carbide and a Ni—Al metallic phase. Example 20 comprises” 8 v/o (Ni, Al), 27.6 v/o B4C and 64.4 v/o Al2O3. U.S. '758 does not appear to specifically recite a hot pressing process for Example 20. PCT Patent Publication WO 92/07102 to Buljan et al. published Apr. 30, 1992) appears to be related to U.S. '758. U.S. Pat. No. 5,279,191 to Buljan appears to disclose an alumina-based ceramic that may include boron carbide. U.S. '191 requires the use of SiC reinforcement and a Ni—Al metal phase.
U.S. Pat. No. 5,162,270 to Ownby et al. pertains to an alumina ceramic that has boron carbide whisker reinforcement. FIG. 1 appears to show specific compositions in which the boron carbide whiskers appear to comprise 0, 5.0, 10.0, 15.0, 20.0 and 30.0 volume percent of the composite (the balance alumina). These samples were hot pressed at 1520° C. under a pressure equal to 7500 psi to achieve a density equal to greater than abut 98 percent of theoretical density. The maximum fracture toughness (about 7.1 MPa·m0.5) occurs at 15.0 volume percent boron carbide whiskers. There is a slight decrease in the fracture toughness (about 7.1 MPa·m0.5 to about 7.0 MPa·m0.5) when boron carbide whisker content exceeds 15 volume percent. U.S. Pat. No. 5,398,858 to Dugan et al. mentions the use of boron carbide whiskers to reinforce alumina. The specific application for the ceramic is in a roller guide.
The article by Liu and Ownby entitled “Densification of B4C Whisker Reinforced Al2O3 Matrix Composites”, Proceedings of the First China International Conference on High-Performance Ceramics (October, 1998, Beijing) pp. 415-419 pertains to the sintering of boron carbide whisker-alumina composites. The boron carbide whisker contents were (in volume percent): 0, 5, 10, 15, 20, 25, 30, 35 and 40.
The article by Liu et al. entitled “Enhanced Mechanical Properties of Alumina by Dispersed Titanium Diboride Particulate Inclusions”, Journal American Ceramic Society 74(1) pp. 241-243 (1991) discloses the use of titanium diboride particles to improve mechanical properties of alumina. FIG. 2 shows the impact of the boron carbide particle content in an alumina-based ceramic on the flexural strength wherein the boron carbide content ranges from 0 to 20.0 volume percent. Like in the other articles to Liu et al., the flexural strength appears to level off (or remain steady) for boron carbide contents that exceed 5.0 volume percent.
U.S. Pat. No. 4,745,091 to Landingham discloses an alumina-based ceramic that has a nitride modifier (e.g. AlN or Si3N4) and dispersion particles. A listing of the dispersion particles mentions boron carbide. According to the '091 Patent, the nitride modifier can range from 0.1 to 15.0 weight percent, and the dispersion particles can range between 0.1 and 40.0 weight percent. There do not appear to be any actual examples that use boron carbide as dispersion particles.
U.S. Pat. No. 6,417,126 B1 to Yang discloses an alumina-based composite with a boride (e.g., boron carbide) and metal carbide (e.g., silicon carbide). The examples appear to disclose compositions comprising alumina, silicon carbide, and boron carbide wherein the boron carbide ranges between 0.5 and 5.4 weight percent. U.S. '126 appears to disclose that the principal use of the ceramic is an industrial blast nozzle. U.S. Patent Application Publication US2002/0195752 A2 to Yang appears to be related to U.S. '126. European Patent 0 208 910 to Suzuki et al. appears to disclose the use of boron carbide along with SiC whiskers in an alumina composite.
U.S. Pat. No. 5,164,345 to Rice et al. relates to an alumina-boron carbide-silicon carbide composite. The end product is the result of heating silicon dioxide, boron oxide, aluminum and carbon.
The article by Sato et al., “Sintering and Fracture Behavior of Composites Based on Alumina-Zirconia (Yttria)—Nonoxides”, Journal de Physique, Colloque C1, Supplement No. 2, Tome 47, February 1986 pp. C1-733 through C1-737 pertains to the sintering of alumina-containing composites including an alumina-zirconia-boron carbide composite. Table 1 of Sato et al. shows various properties of a 50 volume percent Al2O3—40 volume percent ZrO2 (no yttria)—10 volume B4C composite, and an 80 volume percent Al2O3—10 volume percent ZrO2 (no yttria)—10 volume percent B4C composite. Each composite was hot pressed at 1500° C. and 2 GPa for a duration of 30 minutes.
The article by Becher entitled “Microstructural Design of Toughened Ceramics” Journal American Ceramic Society 74(2) pp. 255-269 (1991) discusses toughening mechanisms. The principal toughening mechanism is crack-bridging. Additives include silicon carbide whiskers, tetragonal zirconia and monoclinic zirconia.
U.S. Pat. No. 4,474,728 to Radford and U.S. Pat. No. 4,826,630 to Radford each discloses pellets that comprise alumina and boron carbide. These pellets appear to be useful as neutron absorbers.
While there have been ceramic bodies that comprise alumina and boron carbide, there remains a need to provide an improved ceramic body that contains alumina and a boron carbide phase. There also remains the need to provide a method of making, as well as a method of using such an improved ceramic body that contains alumina and boron carbide. Further, there also remains the need to provide such a ceramic body of alumina and boron carbide that exhibits properties that are especially useful for metalcutting. In addition, there remains a need to provide a method of making (and a method of using) such a ceramic body of alumina and boron carbide that exhibits properties especially useful for metal cutting.
Exemplary of these properties is the ability of the ceramic body to maintain its hardness even at higher operating temperatures, especially those temperatures associated with higher cutting speeds. Another exemplary property is the ability of the ceramic body to exhibit good chemical resistance with respect to the workpiece material even at high operating temperatures, especially those associated with higher cutting speeds.
Each one of these properties by itself, and especially when combined together, provide for a ceramic body that is particularly useful as a ceramic cutting insert for applications at higher cutting speeds wherein there are generated higher operating temperatures. For example, a higher cutting speed contemplated by applicants for ductile cast iron could be a speed equal to or greater than about 1500 surface feet per minute (about 457 surface meters per minute), and more preferably, a higher cutting speed equal to or greater than about 2000 surface feet per minute (610 surface meters per minute).
We have found that hot pressing is one method that has been used to make the above ceramic body containing alumina and boron carbide. Hot pressing has produced ceramic bodies, which contain alumina and boron carbide, that exhibit acceptable properties including properties that make the ceramic body particularly useful for metalcutting.
While the hot-pressing process has produced an acceptable ceramic material, the hot-pressing process typically has experienced drawbacks. One of these drawbacks is associated with the high cost to perform the hot-pressing process. Such a high cost increases the overall cost to produce the ceramic body, and especially a ceramic used as a metalcutting insert. Another of these drawbacks was the inability of the hot-pressing process to permit the cost-effective fabrication of parts that presented a complicated or complex shape or geometry. Such hot pressing is thus not cost-effective for the fabrication of parts with a complicated or complex shape. It would be advantageous if the scope of applicable products for the alumina-boron carbide ceramic would be such to include being fabricated by cost-effective methods.
Thus, another process to densify a powder compact would be sintering including pressureless sintering. Pressureless sintering would be a more desirable process as compared to hot-pressing because of the lower cost associated therewith, as well as the ability of the pressureless sintering process to fabricate in a cost-effective fashion parts with a complicated or complex shape or geometry. However, heretofore, the pressureless sintering of alumina-boron carbide powder compacts had difficulty in achieving closed porosity due to the loss of boron during sintering.
It is apparent that it would be highly desirable to provide an alumina-boron carbide ceramic and a process of making the same that is not as expensive to perform as compared to hot-pressing. If such a process were available, there would be expected to be a decrease in the overall cost to produce the ceramic body.
It is also apparent that it would be highly desirable to provide an alumina-boron carbide ceramic and a process of making the same wherein the process provides for the ability to fabricate in a cost-effective fashion parts with a complicated or complex shape or geometry. If such a process were available, there would be an increase in the scope of applicable products for the alumina-boron carbide ceramic.
It becomes apparent that it would be highly desirable to provide a sintered alumina-boron carbide ceramic body, as well as a sintering process to make an alumina-boron carbide ceramic body that exhibits acceptable properties including acceptable properties that make it suitable for use as a metalcutting insert.